1. Technical Field
The present invention relates to a composite sensor and electronic device housing sensor elements, such as an acceleration sensor element and a vibration type angular velocity sensor, in the same package.
2. Related Art
Sensor elements used for composite sensors differ in sizes or optimum use environment depending on the kinds thereof. For example, a low Q value is required for an acceleration sensor element detecting a movement of a movable section from a point view of a transient response or a shock resistance. In contrast, a higher Q value is required for a vibration type angular velocity sensor element as compared to the acceleration sensor element. Both sensor elements include movable sections. The Q value is designed by utilizing viscosity of a gas surrounding the sensor element. The pressure surrounding the sensor element, thus, needs to be changed for attaining the designed Q.
Specifically, the acceleration sensor element needs to be sealed at around the atmospheric pressure because a dumping effect by the gas is utilized while the vibration type angular velocity sensor element needs to be sealed at a depressurized state in order no to be affected by the gas.
In addition, the size of the acceleration sensor element is generally smaller than that of the vibration type angular velocity sensor element because of its structure.
Composite sensors are known that include an acceleration sensor element and an angular velocity sensor element in the same package. Refer to JP-A-2002-5950 (page 4 and FIG. 1), for example.
Another composite sensor is also known in which an acceleration sensor chip (element) and an angular velocity sensor chip (element) are disposed on the same substrate. Refer to JP-A-10-10148 (page 3, and FIG. 1), for example.
The composite sensor including the acceleration sensor element and the angular velocity sensor element in the same package has a structure withstanding external shocks. However, the pressure of the gas surrounding each sensor element is not adjusted to the optimum value. Accordingly, if the whole package is sealed at the atmospheric pressure, the Q value of the angular velocity sensor element is lowered, deteriorating the characteristics. On the other hand, if the whole package is sealed at a depressurized state, the Q value of the acceleration sensor element is increased, deteriorating the transient response characteristic. The composite sensor in which the acceleration sensor element and the angular velocity sensor element are disposed on the same substrate can be provided with a small size and low costs. However, the pressure of the gas surrounding each sensor element is also not adjusted to the optimum value.
Further, a plurality of spaces having different pressures provided in one package causes a leak between spaces having different pressures. It is thus difficult to control the fluctuation of the characteristics in a long period of time.